Shengzhang Xue

Growth of Spirulina platensis enhanced under intermittent illumination.

The growth characteristics of microalgae under different light conditions (continuous or intermittent) are essential information for photobioreactor design and operation. In this study, we constructed a thin-layer (10mm) flat plate photobioreactor device with a light/dark (L/D) alternation system to investigate the growth of Spirulina platensis under two different light regimes: (1) continuous illumination in a wide range of light intensities (1.00-77.16 mW cm(-2)); (2) intermittent illumination in medium frequency (0.01-20 Hz). Specific growth rate and light efficiency based on biomass production were determined for each round of experiment. Four regions (light limited region, intermediate region, light saturated region and light inhibition region) were recognized according to the results under continuous illumination. Under intermittent illumination, when L/D frequency increased from 0.01 Hz to 20 Hz, specific growth rate and light efficiency were enhanced. However, the enhancement was different, depending on the applied light intensity and light fraction. The higher the light intensity, the greater the enhancement would be when L/D frequency increased from 0.01 Hz to 20 Hz; and the higher the light intensity, the lower the light fractions is needed to maintain light efficiency as high as that under continuous illumination in light limited region.

A novel photobioreactor structure using optical fibers as inner light source to fulfill flashing light effects of microalgae

In this work, a novel photobioreactor structure using optical fibers being fixed vertically to culture flow direction as inner light source was proposed to fulfill flashing light effects (FLE) of microalgae, so as to obtain high light efficiency. Three types of optical-fiber photobioreactor fulfilling FLE of microalgae, i.e. air-driven panel, pump-driven panel and stirred tank type, were proposed and a 130 L airlift panel one was practically constructed on which both cold (light profile, liquid velocity) and hot model tests were carried out. Results demonstrated that it could produce uniformed light/dark frequencies being over 10 Hz and microalgae productivity increased by 43% and 38% for Spirulina platensis and Scenedesmus dimorphus respectively, compared with the control. This suggested the structure to be a viable and promising option for future photobioreactors.

Installation of flow deflectors and wing baffles to reduce dead zone and enhance flashing light effect in an open raceway pond

To reduce the dead zone and enhance the flashing light effect, a novel open raceway pond with flow deflectors and wing baffles was developed. The hydrodynamics and light characteristics in the novel open raceway pond were investigated using computational fluid dynamics. Results showed that, compared with the control pond, pressure loss in the flow channel of the pond with optimized flow deflectors decreased by 14.58%, average fluid velocity increased by 26.89% and dead zone decreased by 60.42%. With wing baffles built into the raceway pond, significant swirling flow was produced. Moreover, the period of average L/D cycle was shortened. In outdoor cultivation of freshwater Chlorella sp., the biomass concentration of Chlorella sp. cultivated in the raceway pond with wing baffles was 30.11% higher than that of the control pond.

On-line modeling intracellular carbon and energy metabolism of Nannochloropsis sp. in nitrogen-repletion and nitrogen-limitation cultures

In this study, a photobioreactor cultivation system and a calculation method for on-line monitoring of carbon and energy metabolism of microalgae were developed using Nannochloropsis sp. in nitrogen-repletion and nitrogen-limitation cultures. Only 30-60% of carbon fixed in Calvin cycle was used for biomass and the rest was lost in light respiration. The net fixed carbon was assumed to be incorporated into protein, lipids, carbohydrates, and nucleic acids, whose contents calculated on-line fitted well with the experimental measurements. Intracellular ATPs were quantitatively divided for biomass production and cell maintenance, and the result is in accordance with known reports. Due to light limitation induced by high cell concentration in batch cultures, the proportion of CO2 loss in light respiration and the proportion of energy for maintenance rapidly increased in culturing process. Nitrogen starvation reduced the light respiration, thus decreasing CO2 loss and maintenance energy, but no effect on ATP requirement for cell growth.

A novel low-cost thin-film flat plate photobioreactor for microalgae cultivation

In this study, a novel thin-film flat plate photobioreactor (FPPBR) mounted with baffles and a 61.2 m2 (2,000 L) photobioreactor system based on the FPPBR were developed. The flow of the fluid in the thinfilm photobioreactor was investigated by means of computational fluid dynamics (CFD). The cultivation of Chlorella sp. and Scenedesmus dimorphus in the thin-film FPPBR was carried out outdoors. The results showed that the flow of culture medium in different channels was uniform. In outdoor cultivation, the biomass productivity in the FPPBR with baffles was 25.2% higher than that in the FPPBR without baffles. In the pilot-scale FPPBR system, the maximum area productivity of Scenedesmus dimorphus reached 21.9 g/m2/day. When the service time of the photobioreactor was 1 and 3 years, the capital cost of the photobioreactor was 4.72 and 2.45

Utilisation of tris(hydroxymethyl)aminomethane as a gas carrier in microalgal cultivation to enhance CO2 utilisation and biomass production

kgalgae, respectively. The results demonstrated that the thin-film FPPBR was cost effective, and it has the potential to be used for mass cultivation of microalgae.

Improved antifouling properties of photobioreactors by surface grafted sulfobetaine polymers

CO2 supplementation is usually a limiting factor in microalgal culture systems, especially when flue gases are used as the carbon source. In this study, tris(hydroxymethyl) aminomethane (THAM) was applied as a gas carrier to increase CO2 storage capacity in the culture medium and enhance microalgal biomass production. Abiotic experiments showed that the amount of CO2 absorbed by the medium within the same absorption time increased with increasing THAM concentration, and the gas absorptivity maintained a higher level (> 60%) under the neutral pH conditions. Cell growth in shaker flasks illustrated that the biomass productivities of Scenedesmus dimorphus were significantly improved (31 to 66%) when the medium contained 2-8 mmol L-1 THAM. Meanwhile, THAM was not biodegraded during the cultivation. The biomass productivities achieved with 6 mmol L-1 THAM were much higher (32 to 33%) than that with routine culture when it was applied into an open raceway reactor system (2 m(2)), and the CO2 utilisation efficiency also increased by 6 to 12%. The results show that the addition of THAM as a gas carrier for enhancing CO2 input could be an easy-to-use and cost-effective approach for mass cultivation of microalgae.

Study of hydrodynamic characteristics in tubular photobioreactors

Abstract To improve the antifouling (AF) properties of photobioreactors (PBR) for microalgal cultivation, using trihydroxymethyl aminomethane (tris) as the linking agent, a series of polyethylene (PE) films grafted with sulfobetaine (PE-SBMA) with grafting density ranging from 23.11 to 112 μg cm−2 were prepared through surface-initiated atom transfer radical polymerization (SI-ATRP). It was found that the contact angle of PE-SBMA films decreased with the increase in the grafting density. When the grafting density was 101.33 μg cm−2, it reached 67.27°. Compared with the PE film, the adsorption of protein on the PE-SBMA film decreased by 79.84% and the total weight of solid and absorbed microalgae decreased by 54.58 and 81.69%, respectively. Moreover, the transmittance of PE-SBMA film recovered to 86.03% of the initial value after cleaning, while that of the PE film recovered to only 47.27%. The results demonstrate that the AF properties of PE films were greatly improved on polySBMA-grafted surfaces.